The invention concerns a film, in particular a stamping film, laminating film or sticker film, which has at least one optically anisotropic layer comprising an at least partially oriented liquid crystal material.
EP 1 227 347 describes aligning liquid crystal polymers (=LCP) on a photopolymer layer and in that way generating a security feature which can be recognised by means of a polariser.
A first orientation layer is printed out on a substrate by means of an ink jet printer, the orientation layer comprising a photopolymer which can be aligned in a given orientation direction by irradiation with polarised light. That layer is now irradiated with polarised light. Then a layer comprising a liquid crystal material is applied to the orientation layer by means of an ink jet printer and conditions are created under which the liquid crystal material is aligned. The liquid crystal material is then hardened by means of UV radiation. Thus, in the region in which the orientation layer comprising a photopolymer and the liquid crystal layer is applied by printing, an anisotropic polymer layer comprising an oriented liquid crystal material is produced whereby the light which is incident in that region is linearly polarised.
In addition EP 1 227 347 describes that two orientation layers can be applied to a substrate in mutually superposed relationship. In that case the two layers are each irradiated with differently polarised light and then fixed so that the result is orientation layers with a differing orientation, which are arranged in mutually superposed relationship. Thus, that multiple coating in combination with a corresponding patterned configuration of the individual, mutually superposed polymer layers makes it possible to produce regions involving differing orientation and thus regions in which the light is linearly polarised in different directions.
In addition WO 01/55960 describes the provision in a security element of a layer comprising a liquid crystal material which is aligned in region-wise manner in different orientation directions. In this case also orientation of the liquid crystal molecules is effected by means of a photopolymer layer which is exposed with linearly polarised light and which serves subsequently for orientation of the liquid crystal molecules prior to cross-linking thereof. In that case regions with a differing alignment of the liquid crystal molecules are arranged in such a way that, in those regions, an object is encoded which is decoded by means of a special associated polariser which also has a corresponding liquid crystal layer which is matched to the security element and which is oriented differently in region-wise manner. In that way it is possible for two different items of image information to be introduced into an optical security element: when the security element is viewed through a ‘normal’ polariser a first latent image is displayed. When the security element is viewed through the above-described polariser which is matched to the security element, with a liquid crystal layer which is oriented differently in region-wise manner—referred to hereinafter as the ‘key’—a second image is decoded and thus rendered visible. A disadvantage with that method is that the security element and the ‘key’ (analyser tool) must be exactly matched to each other and the additional security information can only be retrieved when there is a suitable ‘key’. Production of an appropriate ‘key’ thus involves a similar high level of complication and expenditure to the production of the actual security element.